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Related Experiment Videos

Diffusion in a Fractal System

Makri1, Romanos, Steriotis

  • 1Institute of Physical Chemistry, National Centre for Scientific Research "Demokritos", 153 10 Ag. Paraskevi Attikis, Athens, Greece

Journal of Colloid and Interface Science
|October 3, 1998
PubMed
Summary

The study reveals how water film deposition alters Vycor porous glass geometry. Diffusion behavior shifts from fractal to Knudsen theory depending on whether the porous glass is wet or dry.

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Area of Science:

  • Materials Science
  • Surface Chemistry
  • Physical Chemistry

Background:

  • Vycor porous glass exhibits complex internal surface geometry.
  • Understanding diffusion in porous materials is crucial for various applications.
  • The influence of adsorbed water on porous glass surface properties requires detailed investigation.

Purpose of the Study:

  • To investigate the surface geometry changes in Vycor porous glass.
  • To analyze the impact of water film deposition on diffusion processes.
  • To determine the applicability of different diffusion models (fractal vs. Knudsen) under varying hydration conditions.

Main Methods:

  • Utilized the relative permeability (PR) technique.
  • Employed a H2O/He gas system for measurements.

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  • Analyzed PR curves at different water relative pressures.

    • Main Results:

    • A distinct maximum was observed on the PR curve at a water relative pressure of approximately 0.3.
    • This maximum correlates with geometrical alterations due to water film deposition.
    • Dry conditions showed diffusion best described by fractal systems.
    • Wet conditions indicated diffusion following classical Knudsen theory for smooth cylinders.

    Conclusions:

    • Water adsorption significantly modifies the effective surface geometry of Vycor porous glass.
    • The diffusion mechanism in Vycor glass is dependent on the degree of surface hydration.
    • The study highlights the transition from fractal diffusion in dry conditions to Knudsen diffusion in wet conditions.